Substrate support chucks are widely used to support substrates within semiconductor processing systems. A particular type of chuck used in high-temperature semiconductor processing systems such as high-temperature physical vapor deposition (PVD) and reactive ion etch (RIE) is a ceramic electrostatic chuck. These chucks are used to retain semiconductor wafers, or other workpieces, in a stationary position during processing. Such electrostatic chucks contain one or more electrodes imbedded within a ceramic chuck body.
An electrostatic chuck holds and supports a substrate during a manufacturing process and also removes heat from the substrate without mechanically clamping the substrate. An electrostatic chuck has a structure that includes an electrode in a ceramic base and a surface layer of the electrostatic chuck that is activated by a voltage in the electrode to form an electric charge that electrostatically clamps a substrate to the electrostatic chuck. The electrostatic chuck can further include a plurality of protrusions or projections made from a ceramic material that supports the substrate away from the surface layer. During use of an electrostatic chuck, the back side of a substrate, such as a semiconductor wafer, is held to the face of the electrostatic chuck by an electrostatic force. The substrate is separated from one or more electrodes in the face of the electrostatic chuck by the surface layer of material that covers the electrode. In a Coulombic chuck, the surface layer is electrically insulating, while in a Johnsen-Rahbek electrostatic chuck, the surface layer is weakly conducting. Heat delivered to the substrate during processing can be transferred away from the substrate and to the electrostatic chuck by contact heat conduction with the protrusions and/or by gas heat conduction with a cooling gas. Contact heat conduction is generally more efficient than gas heat conduction in removing heat from the substrate. However, controlling the amount of contact between the substrate and the protrusions can be difficult.
Semiconductor manufacturing operations require that wafer surfaces be as clean as possible. One disadvantage of using a chuck body fabricated from a ceramic material is that, during manufacture of the support, the ceramic material is “lapped” to produce a relatively smooth surface. Such lapping produces particles that can adhere to the surface of the support. These particles are very difficult to completely remove from the surface. Additionally, the lapping process may fracture the surface of the chuck body. Consequently, as the chuck is used, particles can be continuously produced by these fractures. Also, during wafer processing, the ceramic material can abrade the wafer oxide from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere themselves to the underside of the wafer and be carried to other process chambers or cause defects in the circuitry fabricated upon the wafer. It has been found that tens of thousands of contaminant particles may be found on the backside of a given wafer after retention upon a ceramic electrostatic chuck.
Japanese patent application No. 60-261377, published Dec. 24, 1985, discloses a ceramic electrostatic chuck having an embossed support surface. The embossing reduces the surface area of the ceramic support that contacts the wafer. Consequently, the number of contaminant particles transferred to the wafer is reduced. However, such an embossed surface maintains some degree of contact between the ceramic material and the underside of the wafer. Thus, contamination, though reduced, is still substantial.
There is a continuing need for wafer contact surfaces, for example those used in clamping substrates like electrostatic chucks and other articles that support substrates during processing, which minimize the amount of contaminant particles that can be produced and adhere to the underside of the substrate while supported upon the wafer contact surface.